• Geophysics and Geophysical Exploration
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• v.10 no.4
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• pp.377-382
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• 2007

Several prospecting methods have been used to detect deep seated small tunnel in Korea. Tunnel interpretation of seismic method has been performed mainly by wave traveltime inversion method. But it often gives inacurate solution for the exact tunnel position because of the short distance between two measuring boreholes and picking errors of first arrivals. In this study, "error tomogram" was proposed to detect tunnel position and applied to theoretical and field dat using multi-source amplitude data.

• Tunnel and Underground Space
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• v.29 no.2
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• pp.75-88
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• 2019

With Kori nuclear power plant unit 1 as a beginning in April 1978, 24 nuclear power plants have been operated in Korea and two more plants are under construction. As the nuclear power plants being operated, radioactive wastes from the plants have been accumulated so that various methods for disposing them have been proposed. In Korea, researches have been conducted, being focused on DGD (Deep Geological Disposal), however, DBD (Deep Borehole Disposal) method needs considering as an alternative. In this technical note, element technologies for DBD were analyzed by compiling previous researches and their applicability on domestic cases were investigated. Conceptual studies regarding relevant designs were conducted and finally, technical challenges for actual disposal were described.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.2
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• pp.145-155
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• 2010

Recently interest in subsea tunnels is increasing nationwide and the construction of a subsea tunnel is taking place. For the stability of such a subsea tunnel, grouting is necessary for the water barrier and reinforcement of the tunnel. In this study, therefore, it was investigated how the grouting reinforcement had an effect on the stability of a subsea tunnel located in a great depth. To this end, Hydro-mechanical coupled analyses were performed for a sensitivity analysis in terms of different grouting range, rock class, shotcrete thickness, coefficient of lateral earth pressure, grouting thickness, and pumping existence for the rock classes I, III, and V. FLAC-2D ver. 5.0 was used for the numerical analyses. It was came to the conclusion that the effect of the increased water pressure due to the water barrier of the grouting should be considered as well as the strength improved effect in designing grouting reinforcement of subsea tunnels.

• Tunnel and Underground Space
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• v.34 no.4
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• pp.312-329
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• 2024

In various underground research projects such as energy storage and development and radioactive waste disposal targeting deep underground, the characteristics of permeable rock fractures that serve as major pathway of groundwater flow in deep rock aquifer are considered as an important evaluation factor in the design, construction, and operation of research facilities. In Korea, there is little research and database on the location and hydraulic characteristics of permeable rock fractures and the pattern of groundwater flow patterns that may occur between fractures in deep rock boreholes. In this paper, the hydraulic characteristics of permeable rock fractures in deep rock aquifer were evaluated through the analysis of geothermal gradient and pumping test data. First, the deep geothermal distribution was identified through temperature logging, and the geothermal gradient was obtained through linear regression analysis using temperature data by depth. In addition, the hydraulic characteristics of the fractured rock were analyzed using outflow temperature obtained from pumping tests. Ultimately, the potential location and hydraulic characteristics of permeable rock fractures, as well as groundwater flow within the boreholes, were evaluated by integrating and analyzing the geophysical logging and hydraulic testing data. The process and results of the evaluation of deep permeable rock fractures proposed in this study are expected to serve as foundational data for the successful implementation of underground research projects targeting deep rock aquifers.

• Proceedings of the Korean Geotechical Society Conference
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• 2003.06b
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• pp.51-64
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• 2003

Bieniawski에 의해 개발된 RMR은 암석강도 및 불연속면, 지하수 등의 6개 인자에 따라 분류되어, 이들을 합산하여 결정된다. RMR 분류법은 각 요소들에 대한 평가가 비교적 쉽고, 다양한 응용을 거쳐 여러 분야에 적용되어 국내에서도 가장 널리 사용하고 있는 암반분류 방법 중의 하나이다. RMR 분류결과는 터널의 유지시간, 최대 무지보폭의 예측, 지보량 산정, 암반의 물리적 특성값 예측 등에 적용될 수 있다. 또한 RMR 분류법을 사면안정, 댐 기초, 심부 광산 등에 적용하거나, RMR 분류법의 미비한 부분을 보완하기 위한 여러 가지 수정방법이 제시되었다.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.39-47
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• 2003

Rockbursts are mainly caused by a sudden release or the stored strain energy in the rock mass. They have been the major hazard in deep hard rock mines but rarely occur in tunnels. Due to the short history and limited information on rockbursts, the topic has rarely been studied in Korea. Some cases of rockbursts, however, have been reported during construction of a mountain tunnel for waterway. This study focuses on analyzing data on rockbursts obtained from a TBM (Tunnel Boring Machine) tunnel and suggests methods for a comprehensive understanding on rockbursts. From the analysis of the field data of rockbursts, it was found that most rockbursts mainly occurred at the section between the tunnel face and the TBM operating room, and the rock bursting phenomena lasted up to 20 days after excavation in certain areas. The data also show that the bursting spots are located all around the tunnel surface including the face, the wall, and the roof, The maximum size of bursting spots is usually less than 100cm. This study also suggests new scale systems of brittleness and uniaxial compressive strength to evaluate the possible tendency for a rockburst. These systems are scaled based on the scale system of strain energy density. In addition, with these scale systems, this research shows that there are potentially higher tendencies for rockbursts in this specific tunnel. Moreover this research suggests that properties of rock and rock mass, RMR (Rock Mass Rating) value, tunneling method, excavating speed, and depth of tunnel have a strong correlation with rockbursts.

• Journal of the Korean Geotechnical Society
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• v.18 no.5
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• pp.99-108
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• 2002

The nonlinear-brittle-plastic model derived from experiments as well as elastic and elasto-plastic models was applied to the analysis of the rock damaged zone around a highly stressed circular tunnel. The depths of stress redistribution and disturbed zone as well as the characteristic behaviors predicted from each numerical model were compared, As the magnitudes and stress differences of in situ stresses increased, influences of stress redistribution and stress disturbance on un(tiled region of rock mass also intensified. As a result, larger stress redistribution and disturbed zone as well as greater deviatoric stress and displacement were obtained by the nonlinear-brittle-plastic model rather than other conventional models such as elasto-plastic and elastic models. from such results, it was concluded that as the magnitudes and stress differences of in situ stresses increased, larger rock damaged zone might be predicted by the nonlinear-brittle-plastic model. Therefore, it is thought that the damage analysis may be indispensable far highly stressed tunnels.

• Tunnel and Underground Space
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• v.34 no.4
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• pp.330-354
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• 2024

In site characterization of high-level radioactive waste, discontinuity(joint) distribution and rock mass classification, which are key evaluation parameters in the rock engineering field, were evaluated using deep boreholes in the Wonju granite and Chuncheon granite, which belong to Mesozoic Jurassic era. To evaluate joint distribution characteristics, fracture zones and joint surfaces extracted from ATV data were used, and major joint sets were evaluated along with joint frequency according to depth, dip direction, and dip. Both the Wonju and Chuncheon granites that were studied showed a tendency for the frequency of joints to increase linearly with depth, and joints with high angles were relatively widely distributed. In addition, relatively large amounts of weathering tended to occur even in deep depth due to groundwater inflow through high-angle joints. RQD values remained consistently low even at considerable depth. Meanwhile, joint groups with low angles showed different joint characteristics from joint sets with high angles. Rock mass classification was performed based on RMR system, and along with rock mass classification for 50 m intervals where uniaxial compressive strength was performed, continuous rock mass classification according to depth was performed using velocity log data and geostatistical techniques. The Wonju granite exhibited a superior rock mass class compared to the Chuncheon granite. In the 50 m interval and continuous rock mass classification, the shallow part of the Wonju granite showed a higher class than the deep part, and the deep part of the Chuncheon granite showed a higher class than the shallow part.

• 한국지구물리탐사학회:학술대회논문집
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• 1999.08a
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• pp.117-136
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• 1999

The geophysical survey at pre-investigation stage can hardly provide the detailed information on geological structure of site which has difficulty in access and thick overburden. The TSP (VSP applied in tunnel) survey at post-investigation stage can show the detailed geology ahead of tunnel and around cavern. The TSP survey was carried out at the Pyongtaek LPG storage cavern site during the cavern excavation and provided the location and orientation of the fault inferred below Namyangho. In order to confirm the result of TSP survey four boreholes were drilled in access tunnel. The fault was also detected by borehole survey and the location was coincided with the result of TSP survey. Depend on the result of TSP survey and core logging, the design such as cavern layout and length could have been changed. As another case history the TSP survey was performed at the Mumeuje road tunnel which has poor geological information due to thick overburden. The support design was also changed on the base of TSP survey.

• Tunnel and Underground Space
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• v.14 no.4
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• pp.295-303
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• 2004

For the deep underground excavation site with the geological complexity of soft seam and hard rock, the numerical analysis and in-situ measurement on the behaviors of roadway and surrounding rock according to stepwise excavation of the steep soft seam are carried out. The strata behavior is modeled using elasto-plastic FEM considering the empirical failure criteria of Hoek ＆ Brown and the strain-softening model. Hydraulic pressure capsule, MPBX and tape extensometer are installed around the roadway for the in-situ measurement of rock stress and deformation. Despite the complexity of geology and excavation procedure, the elasto-plastic analysis considering the empirical failure criteria of Hoek ＆ Brown and the strain-softening model shows good agreement with the in-situ measurement. Comparison of numerical modeling with in-situ measurement enables to predict the behaviors of the roadway and to obtain design parameters for the excavation and support at depth.